What all this summons into my mind, as I continue the path of free association from T.S. Eliot through my eurypterid to Rhyniognatha, is H.P. Lovecraft's splendid novella, "At the Mountains of Madness" (1936), one of his few genuine science-fiction stories, and a dazzling one.

Gradually the antique types of the Paleozoic fauna died out, and in the Permian rocks are found the last survivors of the cystoid, the trilobite, and the eurypterid, and of many long-lived families of brachiopods, mollusks, and other invertebrates.

But whenever I read it it calls forth for me an image that surely was nothing at all like what Eliot had in mind: that silent sea is, for me, the paleozoic one of the Cambrian or Silurian period of four hundred million years ago, and the owner of that pair of ragged claws is the curious mud-crawling creature known as a _eurypterid, _ a vaguely lobsterish thing that reached lengths of eight feet and more.